TWI516175B - A method to stabilize pressure in a plasma processing chamber, and a program storage medium of same - Google Patents

Description

Method for stabilizing pressure in plasma processing chamber and program storage medium thereof

This invention relates to semiconductor processes, and more particularly to plasma processing.

Advances in plasma processing contribute to the growth of the semiconductor industry. The semiconductor industry is a highly competitive market. The ability of a manufacturing company to handle substrates in different process conditions can make it slightly better than competitors. Therefore, the manufacturing company invests time and resources to identify methods and/or equipment for improving substrate processing.

A typical processing system for performing substrate processing can be a capacitively-coupled plasma (CCP) processing system. This plasma processing system can be constructed and processed in a range of process parameters. However, in recent years, the types of devices that can be processed have become more sophisticated and may require more precise process control. For example, the device to be processed becomes smaller with more subtle features, and for better yield, more precise control of plasma parameters, such as plasma density and uniformity across the substrate, may be required. Pressure control of the wafer region in the etch chamber can be an example of process parameters that affect plasma density and uniformity.

Within a plasma processing chamber, the fabrication of a semiconductor device may require multi-step processing using plasma. During the plasma processing of the semiconductor device, the plasma processing chamber is typically maintained at a predefined pressure for each processing step. As will be appreciated by those skilled in the art, this pre-defined pressure can be achieved via the use of mechanical vacuum pumping, turbopumping, restriction ring placement, and/or combinations thereof.

Conventionally, the valve assembly can be used to regulate the exhaust turbine pump to achieve pressure control to maintain pre-defined pressure conditions in the plasma processing chamber. Additionally or alternatively, the pressure of the plasma generating zone of the plasma processing chamber (e.g., the area encompassed by the two electrodes and the area surrounded by the confinement ring) can be controlled by adjusting the gap between the confinement rings in the confinement ring assembly. This gap is adjusted to control the flow rate of the exhaust gas in the plasma generation zone, thereby affecting the pressure. The total gas flow conducted from the plasma generation zone may depend on several factors, including the number of confinement rings and the size of the gap between the confinement rings, but is not limited thereto.

In view of the need to process the substrate in multiple steps, each of which may involve different pressures, it is desirable to improve the ability to effectively control the pressure in the plasma processing system.

In one embodiment, the invention is directed to a method of stabilizing pressure in a plasma processing chamber. The method includes disposing an upper electrode and a lower electrode for processing a substrate (wherein the upper electrode forms a chamber gap with the lower electrode), and a first mechanism for mechanically coupling with one of the upper electrode and the lower electrode. The method further includes providing a set of restriction rings and a second mechanism configured to mechanically engage the set of restriction rings. The method also includes determining a plurality of conduction curves for different height values of the chamber gap, correlating a limit ring position (CRP) offset value of the set of restriction rings with different height values of the chamber gap, specifying a chamber gap a first height value, moving the first mechanism to adjust the chamber gap to the first height value, determining the first CRP deviation value from the current CRP using the correlation, and using the first CRP deviation value to open loop method Move the second mechanism to adjust the restricted ring group to the new CRP.

The above summary is only one of the many embodiments disclosed herein, and is not intended to limit the scope of the invention, which is set forth in the claims. These and other features of the present invention will be described in more detail by the following detailed description of the invention.

The invention will be described in detail with reference to a few preferred embodiments herein as illustrated in the accompanying drawings. Numerous specific descriptions are set forth to provide a thorough understanding of the invention. It will be apparent to those skilled in the art, however, that the invention may be practiced without some or all of these specific details. In other instances, well known process steps and/or structures have not been described in detail in order to avoid non-essentially.

In accordance with embodiments of the present invention, methods and apparatus for constructing a plasma processing system are provided to enable rapid control of plasma processing parameters. In several plasma processing systems, the chamber gap (i.e., the gap between the upper and lower electrodes) is a recipe parameter and can vary with the steps. In these plasma processing systems, a mechanism for moving the lower electrode assembly to adjust the chamber gap is also provided. In other plasma processing systems, the upper electrode assembly can be moved. In the disclosure herein, it is assumed that the chamber has a movable lower electrode. However, (in addition or in addition) it should be understood that embodiments of the invention herein are equally applicable to the chamber of the movable upper electrode.

When the movement of the chamber gap is required by the formulation, the volume of the plasma generation zone will be changed. This change in volume affects the pressure in this plasma generation zone and requires compensation adjustments for pressure changes. In the prior art, as previously described, controlling the position of the throttle valve upstream of the exhaust turbine pump and/or controlling the position of the restriction ring to change the gap between the restriction rings to achieve pressure control, thereby changing the discharge from the plasma generation zone Gas conduction.

In general, the position of the plug (see 131 of Fig. 1) can be appropriately controlled to adjust the limit ring gap. In the rising stroke of the plug, the gap between the plurality of rings 110a, 110b, 110c, 110d and 110e is enlarged. During the downward stroke of the plug, since the downward movement of the ring 110e is hindered by the lower electrode, and the downward movement of the ring 110d is hindered by the ring 110e or the like, the rings 110a, 110b, 110c, 110d are sequentially rotated from the bottommost ring. Together with the 110e fold. Restricted ring assemblies are well known in the art and will not be described in further detail herein.

When pressure control is required in prior art, a closed loop control system is typically employed. In one example, we measured and/or obtained the pressure in the plasma generation zone, which was then compared to the expected pressure required by the process parameters. Assuming a difference, the plug 131 is appropriately raised or lowered to change the limit ring gap, and the limit gap is controlled via this limit ring to affect the pressure in the plasma generating region. The iterative cycle of these measurements and adjustments is performed step-wise until the desired pressure set point is reached.

This method has proven to be less than satisfactory for chambers with movable electrodes when the prior art method can meet the requirements of a stationary chamber of the electrode system. In these chambers, a sudden change in the volume of the plasma generating zone due to the repositioning of the lower electrode may cause the latching loop pressure to temporarily lose control when the latching loop control algorithm attempts to regain control. Even if the latched loop control algorithm can quickly regain control to begin the adjustment process, the sudden and sudden changes in the pressure caused by the sudden repositioning of the lower electrode may also make the latched loop control algorithm take a considerable amount of time. Time stabilizes the pressure to the desired set point. During this long period of re-stabilization, substrate processing is virtually discontinued. Assuming that the pressure is re-stable for too long, it may damage the capacity.

In an embodiment of the invention, a novel pressure control algorithm is provided to quickly compensate for the large and abrupt changes in the pressure generated by the repositioning of the lower electrode (or upper electrode) in the plasma generation zone. The inventors have learned that for a given pressure, the relationship between the chamber gap (i.e., the distance between the upper and lower electrodes) and the position of the confinement ring (determined by the position of the plug) is slightly (but not precisely) linear. The inventors have also learned that for each chamber gap, the amount of conduction (in liters per second) via the confinement ring is slightly (but not precisely) linearly related to the position of the confinement ring (determined by the position of the plug). relationship.

Furthermore, the inventors have learned that as the gap changes, a rough linear relationship between the amount of conduction and the position of the confinement ring is roughly maintained. By plotting the relative relationship between the conduction and the position of the confinement ring for various chamber gaps, we can show that each conduction curve is substantially linear, and that the number of conduction curves are substantially parallel.

The inventors have learned from these relationships that a rough open loop control strategy can be applied and the parameters of the restriction ring repositioning provided by these relationships can be used to quickly reposition the restriction ring and quickly make the plasma generation zone The pressure is about the expected set point. Once the rough repositioning is done in an open loop, a fine latching loop control strategy can be used to quickly bring the pressure in the plasma generation zone to the desired set point. However, since open loop repositioning is only a rough repositioning, and precise pressure control does not rely on it, it is safe to ignore the non-linearity in the relationship between the conduction of various chamber gaps and the position of the confinement ring. This key embodiment greatly simplifies the calculations and makes the rough open loop relocation method very fast.

In an embodiment, the inventors have inferred that the coarseness of the change in the chamber gap can be quickly accomplished by calculating the offset between the conduction curve and the other and the offset calculated by shifting the position of the limit ring. Pressure compensation. Once this coarse pressure compensation is completed, the locked loop control can then stabilize the pressure to the desired pressure set point. In this manner, pressure compensation is accomplished in two phases: 1) an open loop initial phase in which the limit loop is rapidly moved using the offset value calculated from the previously derived conductance data, and 2) subsequent The loop phase is blocked to reach the derived pressure set point.

The features and advantages of the present invention will become more apparent from the understanding of the appended claims.

1 shows a simplified schematic of a plasma processing system in accordance with an embodiment of the present invention for providing an adjustable gap between an upper electrode assembly and a lower electrode assembly. The plasma processing system 100 can be a single frequency, dual frequency or triple frequency capacitive discharge system, or can be an inductively coupled plasma system or a plasma system that utilizes different plasma generation and/or maintenance techniques. In the example of FIG. 1, the radio frequency may include 2, 27, and 60 MHz, but is not limited thereto.

In the example of FIG. 1, the plasma processing system 100 can be provided with an upper electrode assembly 102 and a lower electrode assembly 104 in an embodiment. The upper electrode assembly 102 and the lower electrode assembly 104 can be separated from one another by a chamber gap 106. The upper electrode assembly 102 can include an upper electrode that is grounded or powered by an RF power source (not shown).

A process gas (not shown) may be supplied to the chamber gap 106 during the plasma processing. The process gas supplied to the chamber gap 106 may be excited to a plasma state by RF power supplied to the lower electrode assembly 104. The plasma in the chamber gap 106 can be confined by the confinement ring assembly 108, which is provided with at least one confinement ring set (110a, 110b, 110c, 110d and 110e). This restriction ring assembly is also provided with a gap control mechanism 112 (including a plug 131) for controlling the gap between the restriction rings (110a-e). The exhaust gas in the chamber gap 106 (i.e., the plasma generating region) may pass through the confinement ring gap between the confinement ring sets (110a-e). Vacuum pumping (not shown to simplify the description) excludes these exhaust gases from the chamber via a throttle valve.

In an embodiment, the lower electrode assembly 104 can be equipped with a piston 114 and an actuation mechanism 116 to allow the lower electrode assembly 104 to move up and down. As a result, the volume within the plasma generation zone can change, resulting in pressure changes that require compensation to limit ring repositioning.

Referring to FIG. 1, when the lower electrode assembly 104 is moved up to conform to the formulation requirements of a predetermined step, the restriction ring assembly 108 can be correspondingly moved in accordance with the movement of the lower electrode assembly 104, thereby changing the gap between the restriction ring assemblies 108. Therefore, not only the sudden change in the volume in the plasma generation zone affects the pressure in the plasma generation zone, but also the variation of the ring gap is also affected.

In order to maintain a predetermined pressure (for example, the pressure already existing before the lower electrode moves), it is necessary to adjust the position of the restriction ring assembly 108 to change the conduction amount of the exhaust gas (unit liter / sec) to compensate for the change in the volume of the plasma generation region and / or limit the change of the ring gap, these changes are caused by the movement of the lower electrode.

2 shows a graph of a restricted loop position (CRP) as a function of chamber clearance for a predefined pressure in accordance with an embodiment of the present invention. Figure 2 is discussed with reference to Figure 1 for ease of understanding.

As shown in Fig. 2, the vertical axis represents the limit ring position of any counting unit. In the implementation, the arbitrary counting unit may be a servo motor index for controlling the servo motor up/down movement of the plug 131. The horizontal axis represents the chamber gap in millimeters (mm). Curve 210 shows the linear relationship between the position of the confinement ring and the chamber clearance for a given pressure.

3 shows a plurality of experimentally derived conduction curves (which illustrate the relationship of conduction to the position of the confinement ring) of different chamber gaps in accordance with an embodiment of the present invention.

As shown in Figure 3, the vertical axis represents the amount of conduction in liters per second (L/s). The horizontal axis represents the limit ring position (CRP) for any counting unit. Curve 310 is a conduction curve for a 1.88 cm (cm) chamber gap. Curve 320 is the conduction curve for the 2.34 cm chamber gap. Curve 330 is the conduction curve for the 2.8 cm chamber gap. Curve 340 is the conduction curve for the 3.1 cm chamber gap.

You can make some observations from Figure 3. First, the curve is substantially linear in the chamber operating zone (i.e., above 4 liters per second). Second, these curves are substantially parallel, which illustrates the linear relationship between the amount of conduction and the position of the confinement ring when the gap is changing. Then, for any given expected conduction (such as 11 liters per second in Figure 3), the limit ring can be moved by the offset of the x-axis (the amount from one curve to the other) to simply compensate for the conduction The change is due to a change in the chamber gap. Referring to Figure 3, when the chamber gap is moved from 2.34 cm (curve 320) to 1.88 cm (curve 310), the limit ring movement can be made equal to the amount of this offset (between point 344 and point 342) to compensate for the conduction. Variety. Limiting the ring to move this amount of deviation (the difference between point 342 and point 344) will have the effect of roughly moving conduction curve 310 to overlap with conduction curve 320. In doing so, we will compensate for the change in conduction due to the change in the gap, and The rough conduction compensation is done in an open loop manner.

In the embodiment, the position of the lower chamber gap can be indicated by "X". The change in chamber clearance can be ± "Y". The current CRP is shown as "A". The new chamber gap and the new CRP can then be calculated according to the following formula: New chamber gap position = X ± Y Equation 1

The new CRP = A ± (M x Y) Equation 2, where M is the slope determined from the conduction curve of Figure 3.

As can be appreciated from the foregoing, a plurality of conduction curves for each of the chamber gaps can be experimentally determined in the examples. The plurality of conduction curves are relatively linear within the conduction range of the operation and are given a slope of approximately M in the embodiment. The offset CRP value can be determined for a predetermined wafer area pressure to compensate for chamber gap adjustment. In addition, the chamber gap can be correlated with the offset value using a simple look-up table method. To facilitate a rough adjustment of the open loop, the corresponding deviation from the value of the particular chamber can be obtained from the values provided by the self-checking method.

4 shows a simplified flow diagram of a method 400 for controlling wafer area pressure as a function of adjustable chamber clearance, in accordance with an embodiment of the present invention.

In step 402, a plurality of different chamber gap conduction curves can be experimentally determined in an embodiment. In step 404, a new chamber gap is designated as part of the process parameters. In step 406, a value that deviates from the current limit ring position can be determined. This deviation value has been discussed earlier when discussing Figure 3. To simplify the calculation and/or look-up table, an optional reference chamber gap can be utilized in embodiments to provide a reference to which all other chamber gaps can be referenced.

Once the offset value is obtained, the offset value can be used to adjust the limit ring position in an open loop manner, and the limit ring is quickly (but roughly) repositioned (step 408). This rapid repositioning roughly compensates for changes in volume in the plasma generation zone and limits changes in the ring gap caused by the movement of the lower electrode. Once the rough repositioning is completed, a fine (but slower) latching loop control (used in the prior art) can be utilized to accurately establish the pressure in the plasma generation zone at the desired set pressure. Once the pressure is re-stabilized, other changes in pressure can be accomplished using techniques known in the prior art (e.g., to accommodate pressure changes in different steps).

As can be appreciated from the foregoing, embodiments of the present invention allow for rapid repositioning of the restraining ring in a two-step process while performing pressure compensation in a rapid manner. In a first step, the limit ring is quickly repositioned using an offset value in an open loop manner, taken from previously obtained conduction data (which correlates the conductance of the various chamber gaps with the limit ring position). In the second step, conventional latching loop control can be used to more accurately stabilize the pressure at the desired value. By quickly compensating for pressure changes caused by moving the electrodes, the pressure stabilization step can be shortened and the productivity can be improved. Moreover, embodiments of the present invention may improve and/or maintain ignition of the plasma as the processing steps progress, each of which may require different chamber gaps and different pressure settings.

Although the present invention has been described in terms of several preferred embodiments, the equivalents of the alternatives, the modifications, the modifications and the various substitutions can be made without departing from the scope of the invention. It should also be noted that there are many alternative ways of performing the methods and apparatus of the present invention. For example, the present invention can be implemented by a program storage medium having a computer readable code embodied therein, and the computer readable code is configured to perform the above method of the present invention. The following additional patent claims are therefore to be construed as being limited to the scope of the inventions

100‧‧‧ Plasma Processing System

102‧‧‧Upper electrode assembly

104‧‧‧ lower electrode assembly

106‧‧‧Cell clearance

108‧‧‧Restriction ring assembly

110a‧‧‧ Ring

110b‧‧‧ Ring

110c‧‧‧ Ring

110d‧‧‧ ring

110e‧‧‧ Ring

112‧‧‧Gap control mechanism

114‧‧‧Piston

116‧‧‧Activity agency

131‧‧ ‧ embolization

210‧‧‧ Curve

310‧‧‧ Curve

320‧‧‧ Curve

330‧‧‧ Curve

340‧‧‧ Curve

342‧‧ points

344‧‧ points

400‧‧‧ method

The present invention is illustrated by way of example in the accompanying drawings, and is not limited thereto, and the same reference numerals in the figures represent like elements, in which: FIG. 1 shows a plasma treatment in accordance with an embodiment of the present invention. A simplified schematic of the system for providing an adjustable gap between the upper electrode assembly and the lower electrode assembly.

2 shows a graph of a restricted loop position (CRP) as a function of chamber clearance for a predefined pressure in accordance with an embodiment of the present invention.

3 shows a plurality of experimentally derived conduction curves (which illustrate the relationship of conduction to the position of the confinement ring) of different chamber gaps in accordance with an embodiment of the present invention.

4 shows a simplified flow diagram of a method 400 in accordance with an embodiment of the present invention, Instantly control wafer area pressure with adjustable chamber clearance.

100. . . Plasma processing system

102. . . Upper electrode assembly

104. . . Lower electrode assembly

106. . . Chamber gap

108. . . Restriction ring assembly

110a. . . ring

110b. . . ring

110c. . . ring

110d. . . ring

110e. . . ring

112. . . Gap control mechanism

114. . . piston

116. . . Actuating mechanism

131. . . embolism

Claims (18)

A method of stabilizing pressure in a plasma processing chamber, the method comprising: providing an upper electrode and a lower electrode for processing a substrate in the plasma processing chamber, the upper electrode forming a chamber with the lower electrode a first mechanism for mechanically combining with the upper electrode and the lower electrode; a set of limiting rings; and a second mechanism for mechanically combining with the limiting ring set; Determining a plurality of conduction curves for different height values of the chamber gap, wherein the plurality of conduction curves account for a relationship of conduction levels for different height values of the chamber gap relative to a confinement ring position (CRP); based on the plurality of conductions a curve that correlates a CRP value of the confinement ring set with the different height value of the chamber gap; assigning a first height value of the chamber gap; moving the first mechanism to adjust the chamber gap to the first a height value; using the correlation step to determine a new CRP value from a current CRP value; moving the second mechanism in an open loop manner to adjust the limit ring group to the new CRP value; and adjusting the limit ring After the plasma processing chamber for providing a pressure regulator with a fine-locked loop mode. A method of stabilizing pressure in a plasma processing chamber as claimed in claim 1 wherein the plurality of conductivity curves are experimentally determined. A method of stabilizing pressure in a plasma processing chamber, as in claim 1, wherein the plurality of conduction curves are substantially linear near an operational conduction value for the purpose of the interrelated step. A method of stabilizing pressure in a plasma processing chamber, as in claim 1, wherein the correlating step is performed for a predetermined substrate region pressure. The method of stabilizing pressure in a plasma processing chamber as claimed in claim 1 further includes selecting a reference value for the chamber gap. The method of stabilizing the pressure in a plasma processing chamber as claimed in item 1 of the patent application. The method wherein the upper electrode is movable. A method of stabilizing pressure in a plasma processing chamber as in claim 1 wherein the lower electrode is movable. A method of stabilizing pressure in a plasma processing chamber as claimed in claim 1 wherein the fine pressure regulation is performed by controlling a turbo pumped exhaust rate. A method of stabilizing pressure in a plasma processing chamber as claimed in claim 1 wherein the fine pressure adjustment is performed by adjusting a gap between the restriction rings. A program storage medium having a computer readable code recorded therein, the computer readable code being executed by a computer to stabilize a pressure in a plasma processing chamber, the plasma processing chamber having a processing substrate The upper electrode, the lower electrode, and the limiting ring set, the program storage medium includes: a first computer readable code for providing a plurality of conduction curves of different height values of a chamber gap formed by the upper electrode and the lower electrode , wherein the plurality of conduction curves illustrate a relationship of conduction levels for different height values of the chamber gap with respect to a confinement ring position (CRP); a second computer readable code for causing the limitation based on the plurality of conduction curves The CRP value of the ring group is associated with the different height values of the chamber gap; a third computer readable code for specifying a first height value of the chamber gap; and a fourth computer readable code for moving one a first mechanism for adjusting the chamber gap to the first height value, the first mechanism being mechanically coupled to one of the upper electrode and the lower electrode; a fifth computer readable code for using the mutual Associated step The CRP value determines a new CRP value from the current CRP value; the sixth computer readable code is configured to move a second mechanism in an open loop manner to adjust the restricted ring group to the new CRP value, the second mechanism Mechanically coupled to the confinement ring set; and a seventh computer readable code for providing fine pressure adjustment to the plasma processing chamber in a latching loop after adjusting the confinement ring set. For example, the program storage medium of claim 10, wherein the experimental determination of the A plurality of conduction curves. The program storage medium of claim 10, wherein the plurality of conduction curves are substantially linear near an operational conduction value for the purpose of the interrelated step. The program storage medium of claim 10, wherein the correlating step is performed for a predetermined substrate area pressure. The program storage medium of claim 10, further comprising a computer readable code for selecting a reference value of the chamber gap. The program storage medium of claim 10, wherein the upper electrode is movable. The program storage medium of claim 10, wherein the lower electrode is movable. The fine pressure adjustment is performed by controlling a turbo pumping exhaust rate as in the program storage medium of claim 10. The fine-grained pressure adjustment is performed by adjusting a gap between the restriction rings as in the program storage medium of claim 10.